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Thread: Rate question

  1. #1

    Rate question

    If 9 cows can eat 4 bales of hay in 5 days, how long will it take 4 cows to eat 17 bales of hay?

    I do not remember how to do this at all

  2. #2
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    Quote Originally Posted by shinimai View Post
    If 9 cows can eat 4 bales of hay in 5 days, how long will it take 4 cows to eat 17 bales of hay?

    I do not remember how to do this at all
    4 bales eaten by 9 cows in 5 days

    1 bale eaten by 9 cows in 5/4 days

    1 bale eaten by 1 cow in 5*9/4 days

    17 bales eaten by 1 cow in 17*5*9/4 days

    17 bales eaten by 4 cows in 17*5*9/(4*4) days
    “... mathematics is only the art of saying the same thing in different words” - B. Russell

  3. #3
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    Quote Originally Posted by shinimai View Post
    If 9 cows can eat 4 bales of hay in 5 days, how long will it take 4 cows to eat 17 bales of hay?

    I do not remember how to do this at all
    This is where the unit analysis will help [and I'm doing it 'upside down from what Subhotosh Khan did, but the answer should be the same]. So the Rate R of using hay is
    R = 4 bales per (9*5 cow-day) = 4 bales / (9*5 cow-day)
    or
    R = (4/45) bales /cow-day
    Thus, at the same rate we want
    R = (4/45) bales /cow-day = 17 bales / (4 * x cow-day)
    or
    x = 17 / 4 / (4/45) = 17 * 45 / 16

  4. #4
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    Is that how you approach all math problems? "Remembering" how to do them? What ever became of thinking?

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